When an electronic device operates, electronic elements inside the device would produce heat. The heat is produced mainly by an operating chip during operation thereof. With the constantly increased performance thereof, the chip's power is now close to 100 W and the temperature thereof would exceed 100° C. if no proper heat dissipation mechanism is provided.
The currently used chips are usually made of a semiconductor material, such as silicon. Since a chip internally includes a large quantity of metal wires and insulating thin films, and the thermal expansion coefficient of the metal wire material might be several times as high as that of the insulating material, the chip would usually crack and become damaged when it continuously works at a temperature higher than 90° C.
To prevent the chip from overheat and burnout, waste heat produced by electric current must be removed from the electronic elements as soon as possible. To quickly remove the produced heat from the chip, the chip is usually arranged to contact with a copper sheet or is embedded in a metal-based ceramic sintered body, such as aluminum-based silicon carbide, which has high thermal conductivity. In addition, a heat-dissipation unit is needed to help increasing the heat dissipation efficiency, so as to avoid an overheated and burnt-out chip. The heat-dissipation unit is mainly a radiating fin assembly, a heat sink or a heat pipe. A cooling fan can also be used to assist in forced convection, in order to achieve desired heat dissipating and cooling effects.
A metal-made heat radiating fin exposed to air would gradually become oxidized to result in electrical potential difference in the radiating fin. Such internal electrical potential difference would in turn cause electrochemical reaction to form metal oxide on the radiating fin. A metal oxide has a thermal conducting efficiency much lower than that of a pure metal, and would therefore largely reduce the heat dissipating effect and thermal conducting efficiency of the metal radiating fin. When the oxidation becomes worse, the oxidized metal oxide having loose structure tends to peel off from the metal surface of the radiating fin to contaminate the chip in contact with the radiating fin.
Further, an oxidized metal surface would change in color to adversely affect the appearance of the metal material.
And, a metal radiating fin formed through metal (such as copper or aluminum) powder sintering process and having a porous structure tends to more easily have reduced heat dissipation performance due to oxidation. To prevent oxidation, the metal radiating fin is usually externally coated with a layer of nickel or tin through a water solution process. The nickel can be coated on the radiating fin in different ways, including electroplating and chemical plating (electroless plating). However, the coating obtained through the water solution process is easily subjected to contamination, such as adsorption of acid group anions, which would corrode the semiconductor packaging.
Further, the nickel coating or the tin coating usually has thermal conducting efficiency much lower than that of the frequently used copper radiating fin, and would therefore have adverse influence on the heat dissipating effect of copper.
It is therefore tried by the inventor to develop a heat-dissipation unit coated with oxidation-resistant nano thin film and a method of depositing such oxidation-resistant nano thin film on the heat-dissipation unit, in order to overcome the drawbacks in the prior art.